Dual intake runner systems can be used with engines to increase torque at different speeds by taking advantage of engine tuning effects. As one example, in mechanically controlled unequal length dual intake runner systems, valves are usually operated synchronously, in phase, where airflow to one intake valve is inhibited by the use of an additional valve in the intake manifold runner. The intake runner valve inhibits flow through the short runner during low speed/low load conditions to improve engine torque and is opened during high speed/load conditions to improve torque as compared to the long intake runner configuration.
However, the inventors herein have recognized a disadvantage with such systems. As one example, the above arrangement may not allow independent control of airflow through the intake runners. Further, the airflow to the short runner cannot be made to lead the airflow to the long runner. Since, in the above systems, the long runner is always flowing, this can degrade performance by limiting the ability to modify cylinder charge motion.
Another method to control intake and exhaust valve operation during engine operation is described in U.S. Pat. No. 6,374,813. This method presents a means to control electromagnetically actuated valves to promote EGR control. The approach selects different valve modes and patterns to regulate internal EGR, i.e., EGR flow through a cylinder as opposed to EGR routed to the intake manifold. Valves are operated independently and control is based on operating conditions of the engine. Further, the disclosure also describes several valve configurations that may be operated in one or more operational modes to promote cylinder air charge swirl.
The inventors herein have recognized that this method may also have a disadvantage. Namely, the method may use a large amount of electrical current to open exhaust valves. Pressure in a cylinder may increase after combustion due to energy release. Accordingly, exhaust valve current may be increased to overcome cylinder pressure during an exhaust stroke. Consequently, higher amounts of electrical current can result in lower fuel economy and electrical system degradation.